Microelectromechanical systems (MEMS) structure to prevent stiction after a wet cleaning process

ABSTRACT

A method for manufacturing a microelectromechanical systems (MEMS) structure with sacrificial supports to prevent stiction is provided. A first etch is performed into an upper surface of a carrier substrate to form a sacrificial support in a cavity. A thermal oxidation process is performed to oxidize the sacrificial support, and to form an oxide layer lining the upper surface and including the oxidized sacrificial support. A MEMS substrate is bonded to the carrier substrate over the carrier substrate and through the oxide layer. A second etch is performed into the MEMS substrate to form a movable mass overlying the cavity and supported by the oxidized sacrificial support. A third etch is performed into the oxide layer to laterally etch the oxidized sacrificial support and to remove the oxidized sacrificial support. A MEMS structure with anti-stiction bumps is also provided.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/615,238, filed on Jun. 6, 2017, which is a Divisional of U.S.application Ser. No. 14/699,070, filed on Apr. 29, 2015 (now U.S. Pat.No. 9,676,606, issued on Jun. 13, 2017). The contents of theabove-referenced patent applications are hereby incorporated byreference in their entirety.

BACKGROUND

Microelectromechanical systems (MEMS) devices, such as accelerometers,pressure sensors, and microphones, have found widespread use in manymodern day electronic devices. For example, MEMS accelerometers arecommonly found in automobiles (e.g., in airbag deployment systems),tablet computers, or in smart phones. For many applications, MEMSdevices are electrically connected to application-specific integratedcircuits (ASICs) to form complete MEMS systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A illustrates a cross-sectional view of some embodiments of amicroelectromechanical systems (MEMS) structure with anti-stictionbumps.

FIG. 1B illustrates an enlarged cross-sectional view of some embodimentsof the MEMS structure of FIG. 1A.

FIG. 2 illustrates a flow chart of some embodiments of a method formanufacturing a MEMS structure with sacrificial supports to preventstiction.

FIGS. 3-14 illustrate a series of cross-sectional views of someembodiments of a MEMS structure at various stages of manufactureaccording to the method of FIG. 2.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

According to some methods for a manufacturing microelectromechanicalsystems (MEMS) device, a first etch is performed into an upper surfaceof a carrier substrate to form a cavity, and a dielectric layer isformed lining the upper surface and the cavity. A MEMS substrate is thenfusion bonded to the carrier substrate through the dielectric layer.Further, a second etch is performed into the MEMS substrate to form theMEMS device with a movable mass overlying the cavity. With the movablemass formed, a cleaning process (e.g., a wet cleaning process) isperformed to remove residual material from the second etch. However, thecleaning process may cause the movable mass to stick to a neighboringsurface in the X, Y, or Z direction. Such stiction, in turn, reducesyields by, for example, about 5%.

In view of the foregoing, the present disclosure is directed to a methodfor manufacturing a MEMS device with a sacrificial support to preventstiction, as well as the resulting MEMS structure. According to themethod, a first etch is performed into an upper surface of a carriersubstrate to form a cavity, and to form the sacrificial support and asacrificial barrier in the cavity. A thermal oxidation process isperformed to oxidize the sacrificial support and the sacrificialbarrier, and to form an oxide layer lining the upper surface andincluding the oxidized sacrificial support and the oxidized sacrificialbarrier. A MEMS substrate is fusion bonded to the carrier substratethrough the oxide layer, and a second etch is performed into the MEMSsubstrate to form the MEMS device with a movable mass overlying thecavity and supported by the oxidized sacrificial support. With themovable mass formed, a cleaning process is performed to remove residualmaterial from the second etch, and a third etch is performed into theoxide layer between the oxidized sacrificial support and the oxidizedsacrificial barrier. The third etch laterally etches the oxide layer,and removes the oxidized sacrificial support and at least part of theoxidized sacrificial barrier, to release the movable mass.

Advantageously, during the cleaning process, the oxidized sacrificialsupport prevents the movable mass from sticking to a lower surface ofthe cavity, and prevents other stiction of the movable mass in the X, Y,and Z directions. This, in turn, increases yields. Further, the oxidizedsacrificial barrier advantageously protects the fusion bond around theedge of the cavity during the third etch. By protecting the fusion bondduring the third etch, yields are further improved. Even more, thethermal oxidation process advantageously leaves anti-stiction bumps inthe carrier substrate along the lower surface of the cavity, and underthe oxidized sacrificial support and the oxidized sacrificial barrier.During the third etch, these anti-stiction bumps are exposed, andsubsequently act as stoppers for the movable mass. The anti-stictionbumps have profiles culminating in points, and therefore reduce thesurface area for the movable mass to stick to and the likelihood ofstiction.

With reference to FIG. 1A, a cross-sectional view 100A of someembodiments of a MEMS structure with anti-stiction bumps 102 a, 102 b isprovided. The anti-stiction bumps 102 a, 102 b are integrated into acarrier substrate 104, and arranged along a surface 106 of the carriersubstrate 104 that is recessed relative to an upper surface 108 of thecarrier substrate 104. Further, the anti-stiction bumps 102 a, 102 bprotrude into a lower cavity 110 defined over the carrier substrate 104.The anti-stiction bumps 102 a, 102 b include one or more centralanti-stiction bumps 102 a arranged within a central region of the lowercavity 110, and/or one or more peripheral anti-stiction bumps 102 barranged at a periphery region of the lower cavity 110 that is laterallypositioned between the central region of the lower cavity 110 andsidewalls of the lower cavity 110. In some embodiments, the centralanti-stiction bump(s) 102 a are line shaped (not visible in thecross-sectional view 100A) and extend in parallel, and/or the peripheralanti-stiction bump(s) 102 b are ring-shaped and arranged around thecentral anti-stiction bumps 102 a. As seen hereafter, the anti-stictionbumps 102 a, 102 b are a by-product of the method used to form the MEMSstructure, and advantageously act as stoppers to reduce stiction betweenthe recessed surface 106 of the carrier substrate 104 and a movable mass112 overlying the lower cavity 110. The carrier substrate 104 may be,for example, a bulk semiconductor substrate, such as a bulk siliconsubstrate, or a silicon-on-insulator (SOI) substrate.

A dielectric layer 114 lines the upper surface 108 of the carriersubstrate 104 around the lower cavity 110, and lines sidewalls of thecarrier substrate 104 that are arranged in the lower cavity 110.Further, the dielectric layer 114 lines the recessed surface 106 of thecarrier substrate 104 around the periphery of the lower cavity 110. Insome embodiments, the dielectric layer 114 has a thickness of about 1micrometer to about 2.5 micrometers. Further, in some embodiments, thedielectric layer 114 includes one or more sacrificial barriers 116. Thesacrificial barrier(s) 116 are arranged over one or more of protrusionsof the carrier substrate 104 extending outward from the recessed surface106 of the carrier substrate 104. For example, in some embodiments, thesacrificial barrier(s) 116 may be arranged over one or more of theperipheral anti-stiction bump(s) 102 b at a periphery of the lowercavity 110. The sacrificial barrier(s) 116 vertically extend from therecessed surface 106 of the carrier substrate 104 to about even with anupper surface 118 of the dielectric layer 114. The sacrificialbarrier(s) 116 are typically ring-shaped shaped (not visible in thecross-sectional view 100A) and extend around the periphery of the lowercavity 110. As seen hereafter, the sacrificial barrier(s) 116advantageously protect the interface between the dielectric layer 114and an overlying MEMS device 120 during manufacture of the MEMSstructure.

The MEMS device 120 is arranged over the dielectric layer 114 and thecarrier substrate 104, and is bonded to the carrier substrate 104through the dielectric layer 114. The MEMS device 120 may be, forexample, a motion sensor, a pressure sensor, or a microphone, andincludes a MEMS substrate 122. The MEMS substrate 122 may be, forexample, a bulk semiconductor substrate, such as a bulk siliconsubstrate, a SOI substrate, or a polysilicon-on-insulator (POI)substrate. In some embodiments, the MEMS substrate 122 may include oneor more springs 124 and the movable mass 112. The spring(s) 124 connectthe movable mass 112 to a peripheral region of the MEMS substrate 122,and suspend the movable mass 112 over the lower cavity 110 and thecentral anti-stiction bump(s) 102 a between the peripheral anti-stictionbump(s) 102 b (i.e., so that the movable mass 112 is laterally offsetfrom the peripheral anti-stiction bump(s) 102 b). In operation, themovable mass 112 deflects in proportion to external stimuli, such asmotion or sound waves, applied to the movable mass 112, whereby theexternal stimuli can be quantified by measuring the deflection. In someembodiments, the deflection is measured using capacitive couplingbetween a movable sensing electrode (not shown) supported by the movablemass 112 and a fixed sensing electrode (not shown) neighboring themovable sensing electrode.

One or more MEMS bond pads 126 and a MEMS bond ring 128 are arrangedover the MEMS substrate 122. In some embodiments, the MEMS bond pad(s)126 and the MEMS bond ring 128 are arranged over upper surfaces 130 ofthe MEMS substrate 122 that are elevated relative to an upper surface132 of the movable mass 112. The MEMS bond ring 128 surrounds an uppercavity 134 defined over the movable mass 112, and typically surroundsthe MEMS bond pad(s) 126. The MEMS bond pad(s) 126 are electricallycoupled to conductors, such as the movable sensing electrode, and/orelectrical circuits arranged within the MEMS substrate 122 and/orunderlying the MEMS substrate 122. The MEMS bond ring 128 and the MEMSbond pad(s) 126 are arranged within one or more bonding layers 136, 138.The bonding layer(s) 136, 138 may be, for example, aluminum, copper,aluminum copper, or germanium.

An integrated circuit (IC) 140 is arranged over the MEMS device 120 andthe upper cavity 134, and bonded to the MEMS device 120. The IC 140supports MEMS operations and may be, for example, anapplication-specific-integrated circuit (ASIC). The IC 140 includes adevice region 142 arranged in an IC substrate 144 of the IC 140 betweena backside 146 of the IC 140 and a back-end-of-line (BEOL) metallizationstack 148 of the IC 140. The device region 142 includes electroniccomponents (not shown), such as, for example, one or more oftransistors, capacitors, resistors, inductors, and diodes. The ICsubstrate 144 may be, for example, a bulk semiconductor substrate or aSOI substrate.

The BEOL metallization stack 148 includes intra-dielectric metallizationlayers 150 stacked within an interlayer dielectric (ILD) layer 152, andan extra-dielectric metallization layer 154 arranged on the ILD layer152, opposite the IC substrate 144. The intra-dielectric metallizationlayers 150 include metal lines 156, and the extra-dielectricmetallization layer 154 includes one or more IC bond pads 158 and an ICbond ring 160. The IC bond pad(s) 158 and the IC bond ring 160 typicallyalign vertically with the MEMS bond pad(s) 126 and the MEMS bond ring128, and bond the IC 140 to the MEMS device 120 therethrough. Contacts162 of the BEOL metallization stack 148 extend from an intra-dielectricmetallization layer 150 to the device region 142. Further, vias 164 ofthe BEOL metallization stack 148 extend between the intra- andextra-dielectric metallization layers 150, 154 to interconnect themetallization layers 150, 154. The ILD layer 152 may be, for example, alow K dielectric (i.e., a dielectric with a dielectric constant lessthan about 3.9) or an oxide. The metallization layers 150, 154, thecontacts 162, and the vias 164 may be, for example, aluminum copper orgermanium.

With reference to FIG. 1B, an enlarged cross-sectional view 100B of someembodiments of the MEMS structure of FIG. 1A is provided. Asillustrated, the anti-stiction bumps 102 a, 102 b of the carriersubstrate 104 have widths tapering into the lower cavity 110. Forexample, the anti-stiction bumps 102 a, 102 b may have a triangularprofile or a semicircular profile. Because the anti-stiction bumps 102a, 102 b have tapering widths into the lower cavity 110, theanti-stiction bumps 102 a, 102 b reduce the surface area for the movablemass 112 (see FIG. 1A) to stick to, and hence reduce the likelihood ofstiction. Further, the anti-stiction bumps 102 a, 102 b have a height Hand a width W1. The height H of the anti-stiction bumps 102 a, 102 b maybe, for example, about 1 micrometer to about 2 micrometers, or about 1micrometer to about 2.5 micrometers. The width W1 of the anti-stictionbumps 102 a, 102 b may be, for example, about 2 to about 4 micrometers,or about 1 to about 5 micrometers.

Also illustrated, the sacrificial barrier(s) 116 are arranged overcorresponding anti-stiction bumps and have a width W2. The width W2 ofthe sacrificial barrier(s) 116 is typically about twice the width W1 ofthe anti-stiction bumps 102 a, 102 b. For example, the width W2 of thesacrificial barrier(s) 116 may be, for example, about 4 to about 8micrometers.

With reference to FIG. 2, a flowchart 200 of some embodiments of amethod for manufacturing a MEMS structure with a sacrificial support toprevent stiction is provided.

At 202, a carrier substrate is provided.

At 204, a first etch is performed into an upper surface of the carriersubstrate to form a sacrificial support and a sacrificial barrier in acavity. The sacrificial barrier is arranged at a periphery of the cavityaround the sacrificial support.

At 206, a thermal oxidation process is performed to oxidize thesacrificial support and the sacrificial barrier. Further, the thermaloxidation process is performed to form an oxide layer lining the uppersurface of the carrier substrate, and including the oxidized sacrificialsupport and the oxidized sacrificial barrier. Advantageously, thethermal oxidation process results in anti-stiction bumps along a lowersurface of the cavity.

At 208, a MEMS substrate is fusion bonded to the carrier substratethrough the oxide layer.

At 210, a chemical mechanical polish (CMP) is performed into the MEMSsubstrate to thin the MEMS substrate.

At 212, a bonding layer is formed over the MEMS substrate.

At 214, a second etch is performed into the bonding layer to form a bondpad and a bond ring over the MEMS substrate.

At 216, a third etch is performed into the MEMS substrate to recess theMEMS substrate around the bond pad and the bond ring.

At 218, a fourth etch is performed into the MEMS substrate to form aMEMS device, including a movable mass supported over the cavity by theoxidized sacrificial support.

At 220, a wet cleaning process is performed to remove residue from thefourth etch. Advantageously, the support structure fixes the position ofthe movable mass during the wet cleaning process, thereby preventingstiction in the X, Y, and Z directions during the wet cleaning process.

At 222, a fifth etch is performed into the oxide layer to laterally etchthe oxide layer between the oxidized sacrificial barrier and theoxidized sacrificial support, and to remove the oxidized sacrificialsupport. Advantageously, the oxidized sacrificial barrier protects thefusion bond around the edge of the cavity while laterally etching awaythe oxidized sacrificial support.

At 224, an integrated circuit is eutectically bonded to the MEMSsubstrate through the bond pad and the bond ring.

While the method described by the flowchart 200 is illustrated anddescribed herein as a series of acts or events, it will be appreciatedthat the illustrated ordering of such acts or events are not to beinterpreted in a limiting sense. For example, some acts may occur indifferent orders and/or concurrently with other acts or events apartfrom those illustrated and/or described herein. Further, not allillustrated acts may be required to implement one or more aspects orembodiments of the description herein, and one or more of the actsdepicted herein may be carried out in one or more separate acts and/orphases.

With reference to FIGS. 3-14, cross-sectional views of some embodimentsof a MEMS structure at various stages of manufacture are provided toillustrate the method of FIG. 2. Although FIGS. 3-14 are described inrelation to the methods, it will be appreciated that the structuresdisclosed in FIGS. 3-14 are not limited to the methods, but instead maystand alone as structures independent of the methods. Similarly,although the methods are described in relation to FIGS. 3-14, it will beappreciated that the methods are not limited to the structures disclosedin FIGS. 3-14, but instead may stand alone independent of the structuresdisclosed in FIGS. 3-14.

FIG. 3 illustrates a cross-sectional view 300 of some embodimentscorresponding to Act 202. As illustrated, a carrier substrate 104′ isprovided. The carrier substrate 104′ may be, for example, a bulksemiconductor substrate, such as a bulk silicon substrate, or a SOIsubstrate.

FIG. 4 illustrates a cross-sectional view 400 of some embodimentscorresponding to Act 204. As illustrated, a first etch is performed intothe carrier substrate 104′ (see FIG. 3) to form a lower cavity 110′, andto form one or more sacrificial supports 402 and one or more sacrificialbarriers 116′ in the lower cavity 110′. The sacrificial support(s) 402and the sacrificial barrier(s) 116′ extend into the lower cavity 110′from a lower surface 106′ of the lower cavity 110′. In some embodiments,the sacrificial support(s) 402 and/or the sacrificial barrier(s) 116′have widths W₃ of about 2 to about 4 micrometers. Further, in someembodiments, the sacrificial support(s) 402 are line shaped (not visiblein the cross-sectional view 400) and extend in parallel, and/or thesacrificial barrier(s) 116′ are ring-shaped (not visible in thecross-sectional view 400) and surround the sacrificial support(s) 402.The sacrificial support(s) 402 are typically arranged within a centralregion of the lower cavity 110′, and the sacrificial barrier(s) 116′ aretypically arranged along a peripheral region of the lower cavity 110′that is laterally positioned between the central region of the lowercavity 110′ and sidewalls of the lower cavity 110′. For example, thesacrificial barrier(s) 116′ may include a pair of sacrificial barriersarranged on opposing sides of the sacrificial support(s) 402. In someembodiments, a width W4 of the space intermediate the sacrificialsupport(s) 402 and the sacrificial barrier(s) 116′ is about 2micrometers to about 50 micrometers.

The process for performing the first etch may include forming a firstphotoresist layer 404 selectively masking the carrier substrate 104′. Anetchant 406 may then be applied to the carrier substrate 104′ accordingto a pattern of the first photoresist layer 404, thereby forming thesacrificial support(s) 402 and the sacrificial barrier(s) 116′ in thelower cavity 110′. After applying the etchant 406, the first photoresistlayer 404 may be removed.

FIG. 5 illustrates a cross-sectional view 500 of some embodimentscorresponding to Act 206. As illustrated, a thermal oxidation process isperformed on the MEMS structure. The thermal oxidation process may beperformed by, for example, exposing the MEMS structure to an oxidizingagent under elevated temperatures.

The thermal oxidation process oxidizes exposed regions of the remainingcarrier substrate 104″ (see FIG. 4), including the sacrificialsupport(s) 402 (see FIG. 4) and the sacrificial barrier(s) 116′ (seeFIG. 4), to form an oxide layer 114′. In some embodiments, the oxidelayer 114′ has a thickness of about 1 micrometer to about 2.5micrometers. The oxide layer 114′ is arranged over the remaining carriersubstrate 104, lines the remaining lower cavity 110″, and includes theoxidized sacrificial support(s) 402′ and the oxidized sacrificialbarrier(s) 116. Typically, the thermal oxidation process about doublesthe widths of the sacrificial support(s) 402 and the sacrificialbarrier(s) 116′. For example, the oxidized sacrificial support(s) 402′and/or the oxidized sacrificial barrier(s) 116 may have widths of about4 about 8 micrometers.

Further, the thermal oxidation process forms anti-stiction bumps 102 a,102 b underlying the oxidized sacrificial support(s) 402′ and theoxidized sacrificial barrier(s) 116. The anti-stiction bumps 102 a, 102b include one or more central anti-stiction bumps 102 a arranged at acenter of the remaining lower cavity 110″ under the oxidized sacrificialsupport(s) 402′. Further, the anti-stiction bumps 102 a, 102 b includeone or more peripheral anti-stiction bumps 102 b arranged at a peripheryof the remaining lower cavity 110″ under the oxidized sacrificialbarriers(s) 116. The anti-stiction bumps 102 a, 102 b have widthstapering into the remaining lower cavity 110″, and typically have atriangular profile or a semicircular profile. In some embodiments, theanti-stiction bumps 102 a, 102 b have a height of about 1 micrometer toabout 2 micrometers, and/or have a width of about 2 to about 4micrometers. As described above, the anti-stiction bumps 102 a, 102 badvantageously serve as stoppers for a movable mass to be formed overthe anti-stiction bumps 102 a, 102 b.

FIG. 6 illustrates a cross-sectional view 600 of some embodimentscorresponding to Act 208. As illustrated, a MEMS substrate 122′ isbonded to the remaining carrier substrate 104 through the oxide layer114′, typically by fusion bonding. The MEMS substrate 122′ may be, forexample, a bulk semiconductor substrate, such as a bulk siliconsubstrate, a SOI substrate, or a POI substrate.

FIG. 7 illustrates a cross-sectional view 700 of some embodimentscorresponding to Act 210. As illustrated, a CMP is performed into theMEMS substrate 122′ (see FIG. 6) to reduce a thickness of the MEMSsubstrate 122′. For example, the thickness of the MEMS substrate 122′may be reduced to about 30 micrometers. In some embodiments, an etchback is additionally or alternatively performed.

FIG. 8 illustrates a cross-sectional view 800 of some embodimentscorresponding to Act 212. As illustrated, one or more bonding layers136′, 138′ are formed stacked over the remaining MEMS substrate 122″.The one or more bonding layers 136′, 138′ may be formed using adeposition process such as spin coating a vapor deposition. Further, thebonding layer(s) 136′, 138′ may be formed of, for example, aluminum,copper, aluminum copper, or germanium.

FIG. 9 illustrates a cross-sectional view 900 of some embodimentscorresponding to Act 214. As illustrated, a second etch is performedinto the bonding layer(s) 136′, 138′ (see FIG. 8) to form one or moreMEMS bond pads 126 and a MEMS bond ring 128 over the remaining MEMSsubstrate 122″. The MEMS bond ring 128 surrounds the remaining lowercavity 110″, and typically surrounds the MEMS bond pad(s) 126. In someembodiments, the MEMS bond pad(s) 126 are electrically coupled toconductors and/or electrical circuits arranged within the remaining MEMSsubstrate 122″ and/or underlying the remaining MEMS substrate 122″.

The process for performing the second etch may include forming a secondphotoresist layer 902 selectively masking the bonding layer(s) 136′,138′. An etchant 904 may then be applied to the bonding layer(s) 136′,138′ according to a pattern of the second photoresist layer 902, therebyforming the MEMS bond pad(s) 126 and the MEMS bond ring 128. Afterapplying the etchant 904, the second photoresist layer 902 may beremoved.

FIG. 10 illustrates a cross-sectional view 1000 of some embodimentscorresponding to Act 216. As illustrated, a third etch is performed intothe remaining MEMS substrate 122″ (see FIG. 9) to recess the remainingMEMS substrate 122″ around the MEMS bond pad(s) 126 and the MEMS bondring 128.

The process for performing the third etch may include forming a thirdphotoresist layer 1002 selectively masking the MEMS bond pad(s) 126 andthe MEMS bond ring 128. An etchant 1004 may then be applied to theremaining MEMS substrate 122″ according to a pattern of the thirdphotoresist layer 1002. After applying the etchant 1004, the thirdphotoresist layer 1002 may be removed.

FIG. 11 illustrates a cross-sectional view 1100 of some embodimentscorresponding to Act 218. As illustrated, a fourth etch is performedinto the remaining MEMS substrate 122′″ (see FIG. 10) to form a MEMSdevice 120, including a movable mass 112 supported over the c by theoxidized sacrificial support(s) 402′ and one or more springs 124.Advantageously, the oxidized sacrificial support(s) 402′ prevent themovable mass 112 from undergoing movement in the X, Y, or Z directions,thereby preventing stiction.

The process for performing the fourth etch may include forming a fourthphotoresist layer 1102 selectively masking the remaining MEMS substrate122′″. An etchant 1104 may then be applied to the remaining MEMSsubstrate 122′″ according to a pattern of the fourth photoresist layer1102. After applying the etchant 1104, the fourth photoresist layer 1102may be removed.

FIG. 12 illustrates a cross-sectional view 1200 of some embodimentscorresponding to Act 220. As illustrated, a cleaning process isperformed to remove residue from the fourth etch. The cleaning processis typically a wet cleaning process, and may include, for example,applying a wet cleaning solution 1202 to the MEMS structure.Advantageously, the oxidized sacrificial support(s) 402′ preventstiction of the movable mass 112 during the cleaning process.

FIG. 13 illustrates a cross-sectional view 1300 of some embodimentscorresponding to Act 222. As illustrated, a fifth etch is performed intothe oxide layer 114′ (see FIG. 12) by exposing the oxide layer 114′ toan etchant 1302 between the oxidized sacrificial support(s) 402′ (seeFIG. 12) and the oxidized sacrificial barrier(s) 116. Typically, theetchant 1302 is a vapor hydrofluoric acid (VHF).

The fifth etch laterally etches the oxide layer 114′ to remove theoxidized sacrificial support(s) 402′, and to expose the centralanti-stiction bump(s) 102 a underlying the movable mass 112. By removingthe oxidized sacrificial support(s) 402′, the movable mass 112 isreleased and becomes movable. Further, the fifth etch at least partiallyremoves the oxidized sacrificial barrier(s) 116 to at least partiallyexpose the periphery anti-stiction bump(s) 102 b. The extent to whichthe oxidized sacrificial barrier(s) 116 are removed may be controlled bythe over etch percentage for the oxidized sacrificial support(s) 402′.The oxidized sacrificial barrier(s) 116 are sacrificed to protect thebond interface between the MEMS device 120 and the remaining carriersubstrate 104 around the edge of the remaining lower cavity 110″. This,in turn, may increase yield by improving the strength of the MEMSstructure.

FIG. 14 illustrates a cross-sectional view 1400 of some embodimentscorresponding to Act 224. As illustrated, an IC 140 is arranged over theMEMS device 120 and bonded to the MEMS device 120. Typically, the IC 140is eutectically bonded to the MEMS device 120 through the MEMS bondpad(s) 126 and the MEMS bond ring 128.

The IC 140 includes a device region 142 arranged in an IC substrate 144of the IC 140 between a backside 146 of the IC 140 and aback-end-of-line (BEOL) metallization stack 148 of the IC 140. Thedevice region 142 includes electronic components (not shown), such as,for example, one or more of transistors, capacitors, resistors,inductors, and diodes. The IC substrate 144 may be, for example, a bulksemiconductor substrate or a SOI substrate. The BEOL metallization stack148 includes intra-dielectric metallization layers 150 stacked within anILD layer 152, and an extra-dielectric metallization layer 154 arrangedon the ILD layer 152, opposite the IC substrate 144. Contacts 162 of theBEOL metallization stack 148 extend from an intra-dielectricmetallization layer 150 to the device region 142. Further, vias 164 ofthe BEOL metallization stack 148 extend between the intra- andextra-dielectric metallization layers 150, 154 to interconnect themetallization layers 150, 154. The ILD layer 152 may be, for example, alow K dielectric or an oxide. The metallization layers 150, 154, thecontacts 162, and the vias 164 may be, for example, aluminum copper orgermanium.

Thus, as can be appreciated from above, the present disclosure providesa MEMS structure. A carrier substrate defines a lower surface of acavity. The carrier substrate includes a first anti-stiction bump and asecond anti-stiction bump arranged along the lower surface. An oxidelayer lines an upper surface of the carrier substrate and sidewalls ofthe cavity. A MEMS device is arranged over the carrier substrate andbonded to the carrier substrate through the oxide layer. The MEMS deviceincludes a movable mass suspended in the cavity over the firstanti-stiction bump and laterally offset from the second anti-stictionbump.

In other embodiments, the present disclosure provides a method formanufacturing a MEMS structure. A first etch is performed into an uppersurface of a carrier substrate to form a sacrificial support in acavity. A thermal oxidation process is performed to oxidize thesacrificial support, and to form an oxide layer lining the upper surfaceand including the oxidized sacrificial support. A MEMS substrate isbonded to the carrier substrate over the carrier substrate and throughthe oxide layer. A second etch is performed into the MEMS substrate toform a movable mass overlying the cavity and supported by the oxidizedsacrificial support. A third etch is performed into the oxide layer tolaterally etch the oxidized sacrificial support and to remove theoxidized sacrificial support.

In yet other embodiments, the present disclosure provides a MEMSstructure. A carrier substrate having a lower cavity arranged within anupper surface of the carrier substrate. The carrier substrate includesan anti-stiction bump arranged along a lower surface of the lowercavity. A MEMS device arranged over the carrier substrate. The MEMSdevice includes a movable mass suspended over the anti-stiction bump. Asacrificial barrier arranged at a periphery of the lower cavity aroundthe anti-stiction bump and the movable mass, and extending from thelower surface of the lower cavity to the MEMS device. An IC arrangedover the MEMS device.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A microelectromechanical systems (MEMS) structurecomprising: a carrier substrate having a top surface and a recessedsurface, wherein the recessed surface is recessed below the top surfaceand is in a cavity that overlies the carrier substrate, and wherein therecessed surface has a first protrusion and a second protrusion; adevice substrate overlying the carrier substrate, wherein the devicesubstrate comprises a movable mass overlying the cavity and the firstprotrusion; and a dielectric layer between and directly contacting thetop surface of the carrier substrate and a bottom surface of the devicesubstrate, wherein the dielectric layer covers the second protrusion andhas a first dielectric portion extending linearly from the secondprotrusion to the bottom surface of the device substrate in a directionorthogonal to the bottom surface of the device substrate, and whereinthe dielectric layer has a sidewall in the cavity and separated from thefirst dielectric portion by a first cavity portion of the cavity.
 2. TheMEMS structure according to claim 1, wherein the carrier substrate andthe first and second protrusions are a semiconductor material.
 3. TheMEMS structure according to claim 1, wherein the dielectric layer is amaterial formed by oxidation of the carrier substrate.
 4. The MEMSstructure according to claim 1, wherein the dielectric layer cups anunderside of the first cavity portion and defines a bottom surface ofthe first cavity portion and a sidewall of the first cavity portion. 5.The MEMS structure according to claim 1, wherein the dielectric layer iscontinuous from the top surface of the carrier substrate to the firstdielectric portion.
 6. The MEMS structure according to claim 1, whereinthe sidewall of the dielectric layer has a ring-shaped top layout thatsurrounds the first protrusion.
 7. The MEMS structure according to claim1, wherein the recessed surface comprises a third protrusion neighboringthe second protrusion, wherein the bottom surface of the devicesubstrate extends continuously and linearly from a location at which thedevice substrate directly contacts the dielectric layer to a locationdirectly over the third protrusion.
 8. A microelectromechanical systems(MEMS) structure comprising: a carrier substrate; a device substrateoverlying the carrier substrate and comprising a mass that is configuredto move within a cavity between the device substrate and the carriersubstrate; and a dielectric layer between the carrier substrate and thedevice substrate, wherein the dielectric layer has a corner portionwrapping around a top corner of the carrier substrate from a top surfaceof the carrier substrate to a first sidewall of the carrier substrate,the first sidewall faces a second sidewall of the carrier substrate,which is on an opposite side of the cavity as the first sidewall and islined by the dielectric layer; the first sidewall and the dielectriclayer extend from the top corner to a recessed surface of the carriersubstrate that is recessed below the top surface and that is in thecavity, and the dielectric layer has a dielectric sidewall extendingfrom the recessed surface to the device substrate at a locationseparated from the first sidewall by a first cavity portion of thecavity and further separated from the second sidewall by a second cavityportion of the cavity.
 9. The MEMS structure according to claim 8,wherein the dielectric layer has a U-shaped portion with a U-shapedprofile that wraps around a bottom of the first cavity portion.
 10. TheMEMS structure according to claim 9, wherein the recessed surface has aprotrusion underlying the U-shaped portion and on an opposite side ofthe first cavity portion as the first sidewall.
 11. The MEMS structureaccording to claim 8, wherein the recessed surface has a protrusiondirectly under the mass and uncovered by the dielectric layer.
 12. TheMEMS structure according to claim 8, wherein the dielectric layer has acolumnar portion that has a columnar profile, that is at the dielectricsidewall, that is in both the first cavity portion and the second cavityportion, and that extends from the recessed surface to the devicesubstrate.
 13. The MEMS structure according to claim 12, wherein thecolumnar portion has a ring-shaped top layout.
 14. The MEMS structureaccording to claim 8, wherein the carrier substrate and the devicesubstrate comprise silicon, and wherein the dielectric layer comprisesoxide.
 15. The MEMS structure according to claim 8, wherein a top cornerof the corner portion directly contacts the device substrate in thefirst cavity portion and is separated from the second cavity portion bythe dielectric sidewall and the first cavity portion.
 16. Amicroelectromechanical systems (MEMS) structure comprising: a substratehaving a top surface and a recessed surface, wherein the recessedsurface is recessed below the top surface and is in a cavity thatoverlies the substrate; a MEMS device overlying the substrate andcomprising a movable mass in the cavity; and a dielectric layer betweenthe substrate and the MEMS device, wherein the dielectric layer extendscontinuously from a first corner of the dielectric layer to a secondcorner of the dielectric layer, wherein the first and second cornersdirectly contact a bottom surface of MEMS device in a first cavityportion of the cavity and are laterally separated by the first cavityportion, wherein the dielectric layer has a line-shaped portion at thesecond corner and with a height equal to a vertical separation betweenthe recessed surface and the MEMS device, and wherein the line-shapedportion is in and between the first cavity portion and a second cavityportion of the cavity.
 17. The MEMS structure according to claim 16,wherein the recessed surface is separated from the first cavity portionby the dielectric layer.
 18. The MEMS structure according to claim 16,wherein the recessed surface has a bump underlying and directlycontacting the line-shaped portion.
 19. The MEMS structure according toclaim 8, wherein the recessed surface of the carrier substrate has asemiconductor protrusion protruding towards the device substrate in adirection, and wherein the dielectric layer extends continuously andlinearly along the dielectric sidewall in the direction from directcontact with the protrusion to direct contact with the device substrate.20. The MEMS structure according to claim 16, wherein the recessedsurface has a protrusion, and wherein the line-shaped portion extendsfrom direct contact with the protrusion to direct contact with the MEMSdevice.